_Range._--From Pacific Coast of Alaska eastward to Atlantic Coast; from northern limit of tree-growth south into central Colorado and northeastern parts of Oklahoma and Georgia. See fig. 47. [Illustration: FIG. 47. Distribution of _Zapus hudsonius_. Guide to subspecies 1. _Z. h. acadicus_ 6. _Z. h. hudsonius_ 2. _Z. h. alascensis_ 7. _Z. h. intermedius_ 3. _Z. h. americanus_ 8. _Z. h. ladas_ 4. _Z. h. campestris_ 9. _Z. h. pallidus_ 5. _Z. h. canadensis_ 10. _Z. h. preblei_ 6. _Z. h. hudsonius_ 11. _Z. h. tenellus_] _Externals._--Size small to medium (total length 188 mm to 216 mm); tail longer than head and body (112 mm to 134 mm) and bicolored, pale brown to brownish-black above, white to yellowish-white below; hind feet long (28 mm to 31 mm), grayish-white above; back ochraceous to dark brown; sides paler than back with dark hair interspersed; lateral line usually present but sometimes indistinct or entirely absent (when present usually clear Ochraceous-Buff); ventral coloration white, sometimes with suffusion of ochraceous; guard hairs average 115 microns (96u to 140u) in diameter; underhair with pigment pattern in form of hollow, narrow rectangles; cuticular scales of underhair large and fewer than those of the underfur of _Z. trinotatus_, but underhair of _Z. hudsonius_ otherwise resembles that of _Z. trinotatus_. _Baculum._--Size small (total length 4.5 mm to 4.9 mm); base medium in width (0.64 mm to 0.72 mm); tip narrow (0.24 mm to 0.26 mm) and dished out in dorsal aspect, blunted; shaft rounded, curving gently upward at tip. _Skull._--Small to medium and relatively narrow in relation to length; rostrum pointed and short; mastoid region relatively narrow; incisive foramina short; base of zygomatic process of squamosal narrow; coronoid process of mandible short, relatively weak. Upper premolar usually small (averaging .30 mm in length and .35 mm in breadth) sometimes functional (most often so in old adults), occlusal surface divided by single shallow re-entrant fold, which in worn teeth forms centrally located lake; tooth-row short as compared to that of other species; individual cheek-teeth usually smaller than those of other species; lower cheek-teeth shorter and narrower than those of other species; angle of mandible strongly inflected. GEOGRAPHIC VARIATION The species _Z. hudsonius_ is divisible into 11 subspecies based on differences in color, relative proportions of the tail, hind feet, body, and size and shape of parts of the skull (zygomata, braincase, incisive foramina, auditory bullae, pterygoid fossae, rostrum, and interorbital breadth). Color of the pelage varies, as a general rule, from dark-backed, dull-sided individuals in the northern parts of the geographic range of the species to light-backed, bright-sided individuals in the southern parts of the range.